Is cold air intake necessary on a turboed car? - Page 5 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-17-2015, 02:00 PM   #81
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Quote:
Originally Posted by speedj View Post
So, the take away answer from my original question is: If I can't get air from a cold source, then at least have an appropriately sized, and properly ducted high efficiency intercooler to deal with the heating issues. Expect to be down on power due to heatsoak issues at the end of your rungroup session, especially on hot days.
And expect to have more coolant temp issues because the average air temp of the air going across your radiator will be higher. Assuming you're normal and your IC is in front of your radiator.
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Old 03-17-2015, 03:18 PM   #82
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Quote:
Originally Posted by speedj View Post
So, the take away answer from my original question is: If I can't get air from a cold source, then at least have an appropriately sized, and properly ducted high efficiency intercooler to deal with the heating issues. Expect to be down on power due to heatsoak issues at the end of your rungroup session, especially on hot days.
Thats what I would take away from this. Also, like Leafy mentioned, this extra heat generated is not ideal. You are adding heat in multiple locations in the engine bay.

If I were you, I would want to find a way to get some cold air, but if it's simply not possible without a lot of expensive routing changes, then don't freak out about it. Keep an eye on all temps, this will likely put larger thermal loads on just about everything.

If you can't CAI, make sure your boost control reference is post-IC!
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Originally Posted by patsmx5 View Post
I have not missed what Scott said. I am well aware of how this stuff works. Just pointed out his error and kindly explained why a CAI is important and not trivial. Apparently the word trivial has different meanings or nobody understands what I write.

Here's a funny things I'll just point out. You guys can read it and just think about it. I'm not going to explain the same thing 20 times and be told I'm wrong when I'm not.

Like you said dustin, a CAI will make the turbo spool faster. Why?

Answer: For the reasons I have explained. When the turbo is "spooling" it doesn't' have enough HP from the turbine yet. So if it's spooling faster with a CAI, that's because the compressor is more efficient. Notice I never said a word about intercooler?
Trust me, I know exactly what you are saying. Without a CAI, you are just making a bunch of entropy, and destroying a ton of exergy. I agree a CAI is not trivial, but it's not huge either. I wouldn't be surprised to see 5+HP increase from adding a CAI to a 220HP car. Expect more if you can safely add timing because the intake charge is a bit cooler. In my opinion, 5 HP in a Miata isn't trivial, but it's not the end of the world either.

Let me try to explain what I mean when I say the difference won't be huge. Assume a non-CAI car and a CAI car are both on side-by-side dynos. Also assume that the non-CAI car owner isn't a complete failure at life and referenced their boost controller after the IC. This is very important. Before the WG opens on both cars, the CAI car will spank the non-CAI car. After both cars are operating at an RPM where the WG is open, the differences will be less apparent. This extra compressor work requirement you are mentioning manifests itself as hotter, less dense air. We both know that. But for a car with an effectively sized IC, then this will just be a larger pressure drop in the IC. If you are speaking of a car that has a boost controller referenced pre-IC, then the power differences will be larger because the extra pressure drop from the IC will not be accounted for. But a post-IC boost control reference will mostly make up for this extra pressure drop, that is the advantage of a post IC boost reference.

Also, if you are speaking of a car with an IC that is optimally sized for an ideal system with a CAI, then the IC would not be able to extract enough heat in the non-CAI system, and what your saying would be true in that case as well. I personally think that more people run an oversized IC than an undersized one, so this isn't super applicable here.

I know that your not mentioning the IC, but the IC and boost control system will very much be masking this effect on a car thats referenced after the IC. Just another reason not to be a fialure and reference your boost controller right after the compressor.

Like Brain mentioned, you'll just be operating on a different path on the turbine map. Not as efficient.

If I were to build a turbo car, I would absolutely run a CAI. People go through a lot of trouble and spend a lot of money to get better spool, it would be stupid to throw some of it away by feeding the compressor hot air.

I realize that this post is entirely too long.
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Old 03-19-2015, 08:05 PM   #83
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For turbo intake length, is shorter better and does having a intake diameter bigger than let's say my 2" t25 inlet make a difference?
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Old 03-19-2015, 08:12 PM   #84
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Intake at least 2x capacity of engine works well in most cases.

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Old 03-19-2015, 08:20 PM   #85
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Sorry my brain no understand
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Old 03-19-2015, 08:29 PM   #86
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Calculate the capacity of the intake between the filter and the turbo, if its smaller than double the engines capacity, make it longer or rounder until it is.

Dann
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Old 03-19-2015, 08:34 PM   #87
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So the diameter of the pipe does not affect performance? So in an ideal world with the same capacity, a t25 with a 2" inlet will flow the same as with a 2" or 3" pipe?
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Old 03-19-2015, 08:36 PM   #88
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Quote:
Originally Posted by Hinano View Post
So the diameter of the pipe does not affect performance? So in an ideal world with the same capacity, a t25 with a 2" inlet will flow the same as with a 2" or 3" pipe?
Come on...
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Old 03-19-2015, 08:39 PM   #89
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I haven't any idea how and to what degree tube diameter and length plays a roll in turbo intake performance.
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Old 03-19-2015, 08:42 PM   #90
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Ive made STUPID power on GT2560's using 2" intake tubes fed by a 3" filter with a venturi moulded into its inside and a 3>2" low angle reducer. But with 2 feet of 2" pipe and >300whp..
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Old 03-20-2015, 09:43 AM   #91
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I've never seen any measureable difference on the dyno with or without an intake tube on 4 differents miatas/setups.

one being an old BEGi Aerodyne setup that had an airbox that uses the stock air filter and litterally a slit for an air source:

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Old 03-20-2015, 11:34 AM   #92
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There is .5 or better percent in power there.. How many times does one need to make a 1% improvement to have a real barn burner?

The intake losses are proportional to velocity (diameter) squared, the length to the first power, the section change from filter to tube and the element losses.

Put a vac gauge in the inlet as close to the compressor as possible. Every inch of vac loss is about 3%.

Measure a stock MSM sometime for a real shocker. Why would they do that?

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Old 03-20-2015, 01:50 PM   #93
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This thread is like a merry-go-round.
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Old 03-20-2015, 02:54 PM   #94
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Quote:
Originally Posted by Corky Bell View Post
There is .5 or better percent in power there.. How many times does one need to make a 1% improvement to have a real barn burner?

The intake losses are proportional to velocity (diameter) squared, the length to the first power, the section change from filter to tube and the element losses.

Put a vac gauge in the inlet as close to the compressor as possible. Every inch of vac loss is about 3%.

Measure a stock MSM sometime for a real shocker. Why would they do that?

corky
http://www.motorsportreg.com/index.c...9#.VQyNXuFMDT8

Hey Corky; have you got a better solution for the air intake on my MSM set-up? Would your MSM CAI box work in combination with the MSM BEIG kit I purchased from you?

I'm leaving tonight for the first Or region SCCA race of the season, running in SPM. So far my rungroup consists of a porsche gt3, a viper, a couple of bimmers and a camaro... I'll be pedaling as fast as I can... so any help with extra power will be appreciated!

Thx for all of your MSM upgrades, they have kept me racing reliably now for many years. craig

Last edited by speedj; 03-20-2015 at 06:16 PM.
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Old 03-20-2015, 06:09 PM   #95
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Quote:
Originally Posted by Corky Bell View Post
Every inch of vac loss is about 3%.

corky
Every inch added to a turbo intake is a 3% loss in what? Flow? How does that translate into actual hp? These maths are way over my head.
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Old 03-20-2015, 08:00 PM   #96
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Quote:
Originally Posted by Hinano View Post
Every inch added to a turbo intake is a 3% loss in what? Flow? How does that translate into actual hp? These maths are way over my head.
Damn son. I dont know where to begin.

Inches of Mercury is a measurement of pressure. In this case a pressure that is lower relative to atmospheric pressure. We call this vacuum. Restriction causes a pressure drop, creating vacuum, which can be measured in inches of Hg using a gauge or MAP sensor.

I think it is reasonable to assume that the intake tube on the inlet of the compressor is isolated from the rest of the system from the effects of resonance, so the length of the tube probably does not matter in that sense. It only matters in that a longer tube may create more restriction. In the same way the volume or diameter of the tube does not matter. All that matters is the flow.

Obviously cold air has some benefit, thats why you see drag cars with turbo inlet in the bumper of the car. Cold, high pressure air going into the turbo is better than hot air in the bay. But does colder air make up for having the turbo breathe through a couple feet of pipe, the way it would have to on a Miata? Thats what this debate really comes down to.
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Old 03-20-2015, 08:19 PM   #97
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Hey thanks man

One question,

how does pressure drop affect performance for a turbo intake? It's not the case that 3% drop = 3% less power is it?
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Old 03-21-2015, 12:10 AM   #98
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@hiano,

measure the diameter of the inlet of your turbo. Your intake pipe should be equal to or greater than that diameter. It should as short and straight as possible (use logic here, longer and more bends = more pressure drop). Cold air source is better than hot air.

That's all the info you need to know. Forget the math stuff if you don't understand it. Just don't choke your turbo before the compressor inlet.
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